1. Field of the Invention
This invention generally relates to network systems and more particularly, to a method and apparatus for upgrading software subsystem stored on a network system.
2. Description of the Related Art
A private branch exchange (PBX) is a telephone switch used to provide telephone service for calls made within a private group or company. Typically, the PBX uses privately leased lines or internal wire or wireless infrastructure to carry calls between a central switching device and the various users. The PBX saves usage charges on calls made entirely within the company by avoiding public telephone networks. Having a PBX also offers a multitude of features and services which can add significant business value to an organization.
Features offered on PBX systems have grown significantly as these telephone switches have become more integrated with computers. To handle incoming calls, automatic call distribution (ACD) map an incoming call to the correct party or parties of an organization. The ACD uses complex algorithms based on utilization, user activity, business rules, and other factors to route the incoming call correctly. Services based on caller line identification (CLID) enable a telephone switch to identify the telephone number of an incoming call, look up corresponding information in a database, and route the call accordingly. For example, the area code of an incoming call can be used to direct an incoming purchase request to the correct sales representative for that region or area. PBX systems are also developing voice processing and voice recognition systems to replace a human agent accessing information through a computer terminal for a particular customer.
Many companies have developed large call centers which utilize these PBX systems to deliver customer service and information. In competitive markets, many companies are able to differentiate their products and the services they provide utilizing sophisticated PBX systems. Often, they must operate 24 hours a day and seven days a week.
A conventional PBX system, such as the Merdian Evolution by Nortel, Inc., includes a central call processor (CP) shelf, a node controller (NC) unit, an access controller (AC) unit and numerous peripheral equipment (PE) devices coupled to handsets, fax modules, or voice processing modules. The CP shelf provides centralized switching capabilities between trunks of users attached to the system through multiple NC devices. The NC units act as large switching devices in directing calls and communicating with the AC units. The CP controls software upgrades by downloading loadware into specific target packs such as the NC unit, the AC units and sometimes even the PE devices. However, it is becoming increasing difficult to upgrade these various controller units without interrupting service or risking extensive downtime.
On conventional systems, upgrades involve downloading the loadware into specific target packs and reprogramming the target pack with new functionality provided in the new loadware. The NC and PE devices are two types of devices referred to as target packs and downloading a loadware module is considered upgrading a pack. Conventional systems upgrade packs using a "cold download" technique which leaves the pack in a disabled state during the upgrade process. The cold download can leave an NC inoperable and also cause calls to be dropped which may be in progress. A new load module can also make the system remain down if the downloaded portion of software is incompatible with the data structures, the communications protocols, or any other portions of the switch. If packs on a PBX were upgraded using a "hot download", the PBX system could be upgraded without significantly interrupting service for existing or new calls.
An upgrade installed incorrectly can be very difficult to uninstall on a conventional PBX. Many aspects of the installation on a conventional PBX cannot be backed out without significant human intervention. If software is incorrectly burnt in flash, the flash-based hardware device may be inoperable and need replacing. Alternatively, software may need to be upgraded manually and not automatically by the system. Either alternative leaves the PBX system down for an extended period of time which can interrupt service and prevent calls from being made.
In light of discussion above, it is desirable to develop an improved system for delivering software upgrades to a private branch exchange (PBX) in switching telephone system.